1. Field of the Invention
The present invention relates to a system and method for speech recognition and its application in robotic systems. More particularly, the present invention relates to a system and method for evaluating the performance of a microphone for long-distance speech recognition in a robot, including mobile robots.
2. Description of the Related Art
In recent years, much attention has been drawn to mobile robots due to the need for health, security, home networks, entertainment, and so on. Mobile robots can perform many tasks that range from tedious to unsafe. In order to operate these mobile robots, human-robot interaction (HRI) is essential. In other words, the mobile robot must be able to recognize the user and to perceive its surroundings by using a robotic vision system so that, like the user, the mobile robot is able to identify the location of the user talking around the robot, as well as to understand commands given by the user.
A mobile robot typically includes a voice input system, which is an essential element for autonomous navigation, as well as for human-robot interaction. Important issues affecting the performance of the voice input system of the mobile robot in an indoor environment include sound and voices from televisions, movies, and computers, as well as noises, reverberations, and the distances which such sounds are projected.
In an indoor environment, there are reverberations of sound due to various noise sources, walls, or other objects. The low frequency component of a human voice has a characteristic that it is attenuated more than the high frequency component according to distance. Therefore, a voice input system that enables an autonomous navigation robot to receive the normal voice of the user at a distance of several meters and to use the received voice directly for speech recognition is required for human-robot interaction in the indoor environment.
In such a voice input system, the choice of microphone is important part of improving the quality of voice and a speech recognition rate. Since a voice input through a microphone must be transduced into electrical signals to provide the voice of the user at a large distance to a feature extraction unit or noise removal unit of a voice recognizer, with as little distortion as possible, an evaluation method for performance comparison of microphones is required.
However, due to the fact that the choice of microphone depends on the characteristics of microphones provided by microphone manufacturers, there is a limitation in evaluating a microphone according to the characteristics of the microphone itself, i.e., the frequency characteristic thereof, the directional characteristic thereof, etc., with respect to a terminal, such as a robot that must be able to receive voices at a large distance.
Therefore, if an input analog voice signal itself is distorted by the microphone, there is no alternative but for the distorted voice signal to be transferred, and also there is no choice but to use the distorted voice signal in the following processing procedures, that is, in an analog/digital conversion procedure, a noise removal procedure, a feature extraction procedure, and so on. For this reason, although a very high-level voice processing algorithm is employed, the possibility of misrecognition in recognizing voices is nevertheless very high.
Meanwhile, as the distance between a microphone and the user increases, it is necessary to increase a gain of a preamplifier to higher and still higher levels in order to recognize voices at a long (increased) distance. However, in this case, there is a known problem in that noise is amplified along with the voice. Therefore, it is necessary to develop an evaluation method for choosing a microphone having a relatively higher sensitivity at a long distance. In the voice at far-talking, in case of the mobile terminal, a distance of considered as far-talking is more than 30 centimeters, and in case of the robot, a distance considered as far-talking is 100 centimeter.
As described above, conventionally, a microphone is chosen only based on the characteristics of microphones provided by the microphone manufacturers. However, in the case of a microphone installed on or in a terminal, such as a robot, the capability of the microphone may not be realized due to volume attenuation according to noises, reverberations, and distance.
In addition, in order for a robot to recognize speech, it is necessary to establish objective evaluation criteria for choosing a microphone which has good sensitivity and can pick up voices at increased distances without distortion increased according to the increased distance.